Integrated process and apparatus for the separation of air

ABSTRACT

In an integrated process for separation of air, an air separation unit produces a stream enriched in oxygen and a stream enriched in nitrogen, the stream enriched in nitrogen is used to liquefy vaporized natural gas by indirect heat exchange and the stream enriched in oxygen is sent to a natural gas treatment unit.

It would be more efficient to reliquefy the low pressure vapors independently of the liquefier.

SUMMARY

According to the invention, a fluid rich in nitrogen generated by the air separation unit (ASU) is used to liquefy the vapors. The same ASU produces oxygen for the reformer process. The ASU has an air compressor which may be driven by steam turbine, using steam from the reformer and/or the synthesis gas process.

The fluid rich in nitrogen may be in liquid form and may be vaporised to condense the vapors of natural gas at low pressure. Alternatively the fluid may be is the form of pressurised gas and may be expanded producing external work to produce a gaseous nitrogen rich stream or a stream which is dual phase, the stream being at a low enough temperature to condense the natural gas vapors.

In this way, a single ASU provides different fluids for different applications on the same site. The energy costs of the liquefaction of natural gas are reduced since no natural gas need be combusted to produce the energy required.

DESCRIPTION OF PREFERRED EMBODIMENTS

Air is compressed in a compressor 1, cooled and purified to form feed stream 3 and sent to air separation unit 100. The air separation unit is of any known kind but in particular may be a cryogenic distillation unit comprised of a single column, a double column or a triple column. The air separation unit produces a liquid nitrogen stream 7 which is sent to a heat exchanger 11 where it exchanges heat with a stream 4 of vaporised natural gas at a pressure of less than 3 bars abs. from a tanker-loading bay 400. The vaporised natural gas 4 is thereby liquefied and returned to the loading bay 400. The air separation unit also produces a gaseous nitrogen stream 9 which is cooled by expanding the gas in a turbine to form a cooled gaseous stream or a dual phase stream. The cooled stream or dual phase stream is sent to a heat exchanger 13 where it is used to liquefy vaporised natural gas coming from the storage tanks of a liquefaction unit 500. The liquefied natural gas 15 is returned to the storage tanks of the liquefaction unit 500. Liquefied natural gas is preferably sent from the liquefaction unit 500 to the tanker-loading bay 400.

Oxygen 24 from the air separation unit is sent in gaseous form to a reformer 200 which is also fed by natural gas 29. Steam 21 produced using the heat generated in the reformer 200 is used to feed a steam turbine 19.

Also present on the site may be a natural gas conversion unit 300 which converts natural gas 27 to synthesis gas. Heat generated by this exothermic reaction may be used to raise steam 23 to be sent to steam turbine 17.

The air compressor 1 may receive power from either or both of steam turbines 17 and 19. 

1-8. (canceled)
 9. A method which may be used for separating air, said method comprising: a) producing an oxygen enriched stream in an air separation unit; b) producing a nitrogen enriched stream in said air separation unit; c) liquefying vaporized natural gas by indirect heat exchange with said nitrogen enriched stream; and d) sending said oxygen enriched stream to a natural gas treatment unit.
 10. The method of claim 9, further comprising expanding said nitrogen enriched stream in a turbine prior to said liquefying.
 11. The method of claim 9, wherein said vaporized natural gas is liquefied at a pressure less than about 3 bar abs.
 12. The method of claim 9, wherein said treatment unit comprises at least one member selected from the group consisting of: a) a natural gas reformer unit; and b) a partial oxidation unit.
 13. The method of claim 9, further comprising compressing feed air for said air separation unit in a compressor, wherein: a) power for said compressor is obtained from at least one steam turbine; and b) said steam turbine is associated with said natural gas treatment unit.
 14. An apparatus which may be used as an integrated air separation unit, said apparatus comprising: a) an air separation unit; b) a conduit for supplying said air separation unit with cooled compressed air; c) a conduit for removing from said air separation unit a nitrogen enriched fluid; d) a conduit for removing from said air separation unit an oxygen enriched fluid; e) a heat exchanger for condensing vaporized natural gas; f) at least one conduit for supplying vaporized natural gas to said heat exchanger; g) at least one conduit for supplying said nitrogen enriched fluid to said heat exchanger; h) at least one conduit for removing condensed natural gas from said heat exchanger; i) at least one conduit for removing a cooled nitrogen enriched fluid from said heat exchanger; and j) a conduit for supplying said oxygen enriched fluid to said natural gas treatment unit.
 15. The apparatus of claim 14, further comprising a turbine located downstream of said air separation unit and upstream of said heat exchanger.
 16. The apparatus of claim 14, wherein said natural gas unit comprises at least one member selected from the group consisting of: a) a natural gas reformer; and b) a natural gas partial oxidation unit. 